Hubble sees back to the beginning

Space telescope reveals shapes of galaxies as they existed 4 billion years ago

WASHINGTON -- In new images from the Hubble Space Telescope, astronomers have for the first time distinguished the shapes of galaxies as they existed in the universe at least 4 billion years ago, before they were violently rearranged by collisions and other forces.

Where before there were blurred images and scientific speculation, the Hubble has revealed pinwheels galore, ellipses, rat-tails, spheres and -- here and there -- the vicious slicing and dicing of one whirling galaxy by another.

It also shows that spiral galaxies like Earth's Milky Way were several times more abundant then than they are now.

In a related discovery some called unexpected and "really tantalizing," the telescope may also have detected in the background of the same image the most distant galactic cluster ever seen, as it existed 10 billion years ago, when scientists believe these dense congregations of stars had just begun to form.

One of the original goals of the Hubble was to help scientists resolve the lingering mystery of how galaxies first formed and by what processes they evolved.

Ground telescopes, looking through Earth's distorting atmosphere, have seen the distant galaxies only as blurry blobs.

After a flaw was discovered in the Hubble's main mirror, astronomers had not expected the orbiting observatory to be able to achieve that mission, at least until the defect is corrected by shuttle astronauts on a flight scheduled for late 1993.

But a team led by Alan Dressler of the Carnegie Institution here used the Hubble's Wide Field-Planetary Camera to accomplish what other astronomers called a difficult feat: They took a continuous exposure of the region for six hours, as the telescope made 10 orbits of the Earth. (After the repair, an exposure one-tenth as long should do the job.)

The resulting image shows Abell 851, a nondescript cluster of some 73 galaxies, each containing perhaps 200 billion stars, found below the bowl of the Big Dipper. The galaxies are so densely packed that they all fit within a spot of sky, as seen from Earth, no more than a quarter of the moon's diameter.

The Abell galaxies are about 4 billion light-years away (which means the light, traveling at 6 trillion miles a year, took 4 billion years to reach the Hubble's camera), or 30 percent of the distance back to the original Big Bang explosion. The image reveals in detail a full range of galactic types: elliptical, spiral and irregular forms, as well as galaxies in collision, ripping each other apart or merging.

"The results have important implications for theories of how galaxies have evolved since the beginning of the universe 15 billion years ago," said Dressler. Finally seeing the shapes, he said, gives scientists "the first unambiguous sign of the influence of environment on the form of a galaxy."

"This one picture validates 20 or 30 years of speculation," said Bruce Margon, of the University of Washington.

Spiral or pinwheel galaxies like our Milky Way are much rarer today than in that younger universe.

Dressler and others said the spirals apparently had their shapes changed by collisions and other consequences of life in what they termed a "Cuisinart environment," where whirling blades of hot gas and gravitational force hold sway.

They said the Milky Way survives as a rare spiral probably because it resides in a less crowded "suburban neighborhood."

Among the images, Dressler also found a quasar (quasi-stellar object) 10 billion light-years away, or 70 percent of the way back to the Big Bang.

These rare objects, the most luminous in the universe, have been spotted before at similar distances. However, this time, the Hubble may have detected the faint "silent majority" of primordial cosmic bodies surrounding them, astronomers said.

These bright spots of light do not resemble the shapes in today's universe at all, Dressler said, and may represent regions of explosive star births.

If so, they could be a major unexpected breakthrough in the study of galactic origins.